CFTR Cl- channel and CFTR-associated ATP channel: distinct pores regulated by common gates.
The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that is regulated by phosphorylation of the R domain and ATP hydrolysis at two nucleotide-binding domains (NBDs). It is controversial whether CFTR conducts ATP or whether CFTR might be closely associated with a separate ATP conductance. To characterize ATP channels associated with CFTR, we analyzed Cl- and ATP single channel-currents in excised inside-out membrane patches from MDCK epithelial cells transiently expressing CFTR. With 100 mM ATP in the pipette and 140 mM Cl- in the bath, ATP channels were associated with CFTR Cl- channels in two-thirds of patches that included CFTR. CFTR Cl- channels and CFTR-associated ATP channels had slope conductances of 7.4 pS and 5.2 pS, respectively, and had distinct reversal potentials and sensitivities to channel blockers. CFTR-associated ATP channels exhibited slow gating kinetics that depended on the presence of protein kinase A and cytoplasmic ATP, similar to CFTR Cl- channels. Gating kinetics of the ATP channels as well as the CFTR Cl- channels were similarly affected by non-hydrolyzable ATP analogues and mutations in the CFTR R domain and NBDs. Our results indicate that phosphorylation- and nucleotide-hydrolysis-dependent gating of CFTR is directly involved in gating of an associated ATP channel. However, the permeation pathways for Cl- and ATP are distinct and the ATP conduction pathway is not obligatorily associated with the expression of CFTR.
Sugita
M
M
Institute for Human Gene Therapy, School of Medicine, University of Pennsylvania, Philadelphia 19104-6100, USA.
Yue
Y
Y
Foskett
J K
JK
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D018118:Chloride Channels / Q000737:chemistry / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000378:metabolism*; D004285:Dogs; D006868:Hydrolysis; D015640:Ion Channel Gating; D007668:Kidney; D009711:Nucleotides / Q000378:metabolism; D010539:Permeability; D010766:Phosphorylation
D002352:Carrier Proteins; D018118:Chloride Channels; D009711:Nucleotides; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000255:Adenosine Triphosphate